Impact-driven frequency-up converter based on high flexibility quasi-concertina spring for vibration energy harvesting

In this paper, an impact-driven frequency-up converter for low-frequency vibration energy harvesting is pro-posed and investigated. Low-frequency vibration presents a significant challenge in vibration energy harvesting, and frequency-up conversion is one of several techniques used to tackle this concern. The proposed design is based on a high-flexibility Quasi-Concertina (QC)-based structure with a resonant frequency of-25 Hz, along with high-frequency piezoelectric cantilevers of a resonant frequency of-250 Hz. The mathematical model describing the operating sequence of the frequency-up conversion approach was initially developed. Experi-mental studies of the manufactured device were also conducted to validate the concept and to evaluate the performance and efficiency of the system under different frequencies, accelerations, and gaps between the QC structure and the piezoelectric cantilevers. The system achieved a peak voltage of 10 V (RMS voltage of 3.40 V) when subjected to vibrations of 2 g@25.5 Hz for an air gap of 2 mm. We also explored the possibility of using four piezoelectric cantilevers. Theoretically, the peak voltage dropped to 16 V; however, the RMS voltage increased to 8.44 V due to the slow damping of the generated output signal. The bandwidth was equal to 24-28 Hz for an acceleration of 1.8 g and 25-27.5 Hz for 1.4 g.